<?php 
if (isset($_GET['a'], $_GET['b'])) {
	$a = (int) $_GET['a'];
	$b = (int) $_GET['b'];
	if ($a > $b) {
		echo "Error: $a > $b!";
		return;
	}
	while ($a <= $b) {
		echo "<tr> <td> $a </td> <td>", $a*$a, "</td> </tr>";
		$a++;
	}
}
?>